Magnetic disk device

ABSTRACT

A magnetic disk device having a magnetic disk for recording information, a rotary mechanism for rotating the magnetic disk, a magnetic head unit for recording information on the rotating magnetic disk, a slider having mounted thereon the magnetic head unit and flying over the rotating magnetic disk, a magnetic head supporting mechanism for supporting the slider, and a positioning mechanism for setting the magnetic head unit at a predetermined radial position. The magnetic head supporting mechanism has mounted thereon an integrated circuit (IC) for amplifying an information write/read signal of the magnetic head unit, and a control circuit is connected to the IC. A record frequency is controlled according to the radial position of the IC on the magnetic disk by the control circuit.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is a continuation of U.S. application Ser. No. 09/859,531,filed May 18, 2001, the subject matter of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a magnetic disk device, and inparticular to a magnetic disk device having a magnetic head supportingmechanism including at least an IC for amplifying information on amagnetic head unit.

[0003] Conventionally, an IC is arranged in opposed relation with a disksurface in order to cool the IC while maintaining the distance of notmore than 1 mm between the disk and the IC as disclosed inJP-A-11-195215.

[0004] Also, JP-A-11-296803 discloses a magnetic disk device in which acontrol circuit connected to an IC, after supplying a write current tothe magnetic head unit for a predetermined length of time, prevents thewrite current from flowing to the magnetic head unit for a suspensiontime not shorter than the particular predetermined length of time.

SUMMARY OF THE INVENTION

[0005] In arranging an IC in opposed relation to the disk surface,various problems are liable to occur. For example, the length of thewiring (flexible print circuit: FPC) laid between the IC and themagnetic head unit is restricted, the disk may be damaged by the IC andthe disk coming into contact with each other under an external shock,and the IC junction facing down makes the pattern inspection (electricalinspection) difficult.

[0006] Also, the cooling effect (ability) of the air flow with the diskrotation is varied with the radial position of the IC. Thus, the timeduring which the continuous write operation can be performed on themagnetic head unit is different depending on the radial position of theIC. If the continuous write time and the suspension time are determinedwithout taking the cooling ability depending on the radial position ofthe IC into account, therefore, the continuous write time may be limitedto a time length which is provided when the IC is located at the innerperipheral position which is low in cooling ability. As a result, theotherwise available continuous write time (ability) based on the highcooling ability with the IC located on the outer peripheral position mayfail to be used, resulting in a reduced utilization rate.

[0007] In order to solve the problems described above, the object of thepresent invention is to provide means for maintaining the temperaturerise of the IC not higher than a tolerable temperature without arrangingthe IC chip in opposed relation to the disk surface.

[0008] According to one aspect of the invention, there is provided amagnetic disk device comprising an IC mounted on a magnetic headsupporting mechanism, for amplifying the information write/read signalon the magnetic head unit, and a control circuit connected with the IC,wherein the power consumption for the write/read operation is controlledin accordance with the head position on the magnetic disk by the controlcircuit thereby to maintain the IC temperature at a level not higherthan a predetermined temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 shows a magnetic head supporting mechanism according to afirst embodiment of the invention.

[0010]FIG. 2 is a block diagram showing the control circuit according tothe first embodiment of the invention.

[0011]FIG. 3 is a diagram showing the relative positions of the head ICand the magnetic disk.

[0012]FIG. 4 is a diagram showing the relation between the thermalresistance and the Reynolds number of rotation.

[0013]FIGS. 5A, 5B and 5C are diagrams for explaining the concept of theduty factor of the conduction time of the IC.

[0014]FIG. 6 is a block diagram showing the control circuit according toa second embodiment of the invention.

[0015]FIG. 7 is a diagram showing the relation between the calorificvalue and the response time according to a third embodiment of theinvention.

[0016]FIG. 8 is a diagram showing the relation between the response timeand the temperature change according to the third embodiment of theinvention.

[0017]FIG. 9 shows a magnetic head supporting mechanism according to afourth embodiment of the invention.

[0018]FIG. 10 is a block diagram showing the control circuit accordingto the fourth embodiment of the invention.

[0019]FIGS. 11A and 11B each show a different magnetic head supportingmechanism according to other embodiments of the invention.

[0020]FIGS. 12A and 12B are diagrams showing a general configuration ofa magnetic disk device with the cover attached and removed,respectively.

DESCRIPTION OF THE EMBODIMENTS

[0021] A first embodiment of the invention will be explained withreference to the accompanying drawings. FIGS. 12A, 12B show a generalconfiguration of a magnetic disk device according to the invention.

[0022] As shown in FIG. 12A, the magnetic disk device is made up of abase 1 in the shape of a box having a magnetic disk and a magnetic headunit accommodated therein and hermetically sealed with a cover 2. Asshown in FIG. 12B, the base 1 is configured to accommodate therein amagnetic disk 4 stacked on a spindle 3, and a positioning mechanism 9including a magnetic head supporting mechanism 5 for supporting themagnetic head unit (not shown), a guide arm 6 coupled to the magnetichead supporting mechanism 5, a pivot bearing 7 and a voice coil motor 8.

[0023] The configuration of the magnetic head supporting mechanism 5 isshown in detail in FIG. 1. FIG. 2 is a block diagram of a signalprocessing circuit for the magnetic head unit. A slider 10 on which themagnetic head unit (not shown) is mounted is supported on a flexure 11.The flexure 11 is coupled to a load beam 18 including a flat portion 12,a flange portion 13 and a spring portion 14. The magnetic head unit isadapted to write or read information by flying over or contacting themagnetic disk 4 rotating in the direction of arrow 17. The other end ofthe load beam 18 includes a guide arm coupler 16 for coupling to theguide arm 6 and an IC mount 19 for mounting a signal amplifier(hereinafter referred to as the IC) 30. The magnetic head supportingmechanism 5 is mounted in such a manner that a cylindrical mounter (notshown) arranged on the guide arm coupler 16 is caulked in the mountinghole 61 of the guide arm 6.

[0024] According to this embodiment, the load beam 18, the guide armcoupler 16 and the IC mount 17 are formed of a single thin plate. Thespring portion 14 is formed with a window 15 for optimizing the springrigidity. The IC 30 is connected to a wiring 31 extending from themagnetic head unit. The wiring 31 reaches the IC 30 from the magnetichead unit through the flexure 11. Also, the wiring from the IC 30 isconnected to a read/write controller 51 as shown in FIG. 2. Theread/write signal is transmitted and received through a HDD controller50 between the magnetic disk device and an external computer not shown.The controllers 50 and 51 are usually incorporated in a circuit insidethe magnetic disk device, but are not limited thereto and can bedisposed anywhere.

[0025] As shown in FIG. 3, the slider 10 moves between the innerperiphery and the outer periphery of the magnetic disk 4. As a result,the radial position of the IC 30 moves from the inner periphery to theouter periphery. Let r be the distance from the center of rotation ofthe magnetic disk and the IC 30. The relation between the distance r andthe power consumption (calorific value) of the IC, and the temperaturerise of the IC with the change in the revolution speed N of the magneticdisk experimentally determined are shown in FIG. 4.

[0026] An explanation will be given in more detail with reference toFIG. 3. The magnetic disk device used in the experiment is 3.5 inchtype. The IC used in the experiment has a heater and a temperaturesensor built therein. The revolution speed is changed between 6000 r/minand 12000 r/min to study the relation between the power consumption andthe temperature rise of the IC. As a result, as shown in FIG. 4, it hasbeen found that all the measurements, organized using the relationbetween the Reynolds number of rotation Rew and the thermal resistanceRh (calorific value w/temperature rise k), can be expressed by thecalculation formula of equation (1).

Rh=a×10⁻⁸×Rew+1.8×10⁻³  (1)

[0027] where Rew =ωr²/v, ω is the angular velocity, v is the kinematicviscosity coefficient, and a is an arbitrary numerical value between 1and 2, or typically 1.6.

[0028] In FIG. 4, the thermal resistance Rh at Rew =0 represents thethermal resistance Rh at the disk rotational speed of 0 (that is, whenthe disk is stationary). In other words, it indicates the thermalresistance due to the two effects including the heat conduction to thestructure and the heat transmission by the natural convection. Also,FIG. 4 shows the thermal resistance Rh of the IC at the inner peripheralposition and the outer peripheral position of the magnetic head unit.From FIG. 4, it is seen that as long as the IC power consumption(calorific value) is the same, Rh is larger and therefore thetemperature rise is smaller on the outer periphery than on the innerperiphery.

[0029] Table 1 shows the Reynolds number Rew of rotation, the thermalresistance Rh and the temperature rise for the power consumption of 400mW on the middle and outer peripheries. TABLE 1 Thermal Temp. rise (K)Calorific value Duty factor (%) Reynolds resistance at power (mW) attemp. at temp. number of (calorific value consumption increase of riseof IC position rotation W/temp rise K) of 400 mW 50 K 50 K Inner  5.3 ×10⁴ 0.0026 160 125 31 periphery Middle  8.1 × 10⁴ 0.0031 129 155 38periphery Outer 12.1 × 10⁴ 0.0037 108 185 46 periphery Remarks Carriedout in Carried out in first second embodiment embodiment

[0030] Table 1 shows that the continuous heating with the powerconsumption of 400 mW causes the IC temperature rise of 160 K on theinner peripheral position, which exceeds the IC junction temperature of120□C. Normally, the temperature in the disk device is expected toincrease up to 70□C., and therefore the tolerable temperature rise ofthe IC is required to be considered as 50 K in maximum. For suppressingthe temperature rise of the IC chip to not more than 50 K, therefore,the power consumption at each radial position is set to 125, 155 and 185mW or less for the inner periphery, the middle periphery and the outerperiphery, respectively, as shown in Table 1.

[0031] Further, the results shown in Table 1, organized by making thepower consumption at the inner peripheral position 1 is shown in Table2. This table indicates that the power consumption on the outerperipheral position is tolerable up to 1.5 times higher. TABLE 1 Temp.rise at Calorific value Duty factor Reynolds 400 mW of power at temp. attemp. number of Thermal consumption rise of rise of IC position rotationresistance 5.3 × 10⁴ 50 K 50 K Inner  5.3 × 10⁴ 1 1 1 1 periphery Middle 8.1 × 10⁴ 1.2 0.81 1.2 1.2 periphery Outer 12.1 × 10⁴ 1.5 0.68 1.5 1.5periphery Remarks Carried out in Carried out in first second embodimentembodiment

[0032] This result shows that according to the first embodiment, the ICpower consumption may be made larger when the IC is located on the outerperiphery than when it is located on the inner periphery of the magneticdisk 4. The difference ΔW in power consumption therebetween may be theone which satisfies the following relation determined by multiplyingequation (1) by the tolerable temperature rise ΔT of the IC.

ΔW≈a×10⁻⁸×(Ro ² −Ri ²)ω/v×ΔT  (2)

[0033] where ω is the angular velocity, vthe kinematic viscositycoefficient of air (2×10⁻⁵m²/s), ΔW the power consumption difference(W), ΔT the tolerable temperature rise, a an arbitrary value between 1and 2, or typically 1.6 and Ro and Ri outer and inner peripherypositions of the IC, respectively.

[0034]FIG. 2 is a block diagram of the control system. As shown in theblock diagram of FIG. 2, a microprocessor 58 calculates the increment ofthe power consumption allowed by the use at the outer peripheralposition Ro with respect to the inner peripheral position Ri, fromequation (4) and the radial position of the head unit IC 52 determinedby an IC position converter 56 in response to a signal from the magnetichead unit 53 (made up of two heads including a write head 54 and a readhead 55), and thereby controls the power supplied to the head IC 52through a read/write controller 51. As a result, even in the case wherethe power supplied to the IC (power consumption) is increased, thetemperature rise of the IC can be suppressed to not higher than thetolerable temperature.

[0035] In FIG. 2, the positioning controller 59 is for setting themagnetic head unit 53 at a predetermined radial position. A spindlecontroller, though not shown, for controlling the rotational speed ofthe magnetic disk is also included in the actual magnetic disk device.Also, the IC has therein a temperature sensor 57 making up a temperaturedetector to cut off the power to the IC in the case where the IC isheated abnormally. Specifically, in the case where the IC has reachedthe junction temperature of 120□ or higher, for example, the datawrite/read operation by the magnetic head unit is suspended. As aresult, the damage to the IC can be prevented. Also, the powerconsumption can also be controlled using the information from thistemperature sensor.

[0036] In the case where the write operation of the magnetic head unitis suspended, the (write) data is stored in the memory of the magneticdisk device (HDD). Thus, the performance of the magnetic disk device asviewed from the personal computer PC can be prevented from decreasing.

[0037] The aforementioned configuration makes it possible to supply theIC with the power commensurate with the cooling ability at the radialposition of the IC. As a result, the power supplied to the IC can beincreased progressively from inner to outer periphery while suppressingthe temperature rise of the IC to a predetermined level. Thus, the ICcapacity can be utilized to maximum. As a specific example, the write(read) frequency (capacity) of the IC, i.e. the read/write speed can beincreased progressively from inner to outer periphery. In this way, theread/write performance of the magnetic head unit can be improved whilekeeping the IC temperature rise within a tolerable range.

[0038] A second embodiment of the invention will be explained withreference to FIGS. 5A, 5B, 5C, 6 and Tables 1, 2. According to the firstembodiment, the optimization of the power consumption of the IC at eachradial position was considered on the assumption that the power (powerconsumption) corresponding to the radial position is suppliedcontinuously to the IC. In the case where the IC is operating normally,on the other hand, a specified power (power consumption) may berequired. According to the second embodiment, therefore, a system isemployed in which the specified operation power is supplied for a shortlength of time to assure normal IC operation, after which a suspensiontime is provided. The ratio between the heating time and the suspensiontime (duty factor) is optimized, so that like in the first embodiment,the rated power is supplied to the IC while suppressing the ICtemperature rise within a predetermined value. As a result, theoperation efficiency of the IC can be maximized. FIGS. 5A, 5B and 5Cshow the concept of the duty factor. In the case where the rated powerconsumption W is required, assume that the conduction time T is reducedto one half so that the suspension time is the same as the conductiontime (i.e. 50% in duty factor). Then, it is thermally (i.e. from theviewpoint of the IC temperature rise) equivalent to the case where thecontinuous heating is carried out with one half of the power consumption(W/2).

Duty factor D=Tw/(Tw+Tk)  (3)

[0039] where Tw is the continuous conduction time, and Tk the suspensiontime.

[0040] In the case where the rated power consumption of the IC is 400mW, therefore, the duty factor thereof may be set to 31%, 38% and 46%for the inner periphery, middle periphery and the outer periphery,respectively, as shown in Table 1. In the case where the duty factor forthe inner periphery is set to unity, on the other hand, the value forthe outer periphery can be set to 1.5 times larger as shown in Table 2.It is thus see that the duty factor for the outer periphery can beincreased beyond the value for the inner periphery and the ratio can beset to about 1.5. As a result, the predetermined rated power can besupplied to the IC while suppressing the IC temperature within thetolerable temperature rise.

[0041]FIG. 6 shows a block diagram for explaining the operation. Thepresent embodiment is different from the first embodiment shown in FIG.2 in that a duty factor calculator 60 corresponding to the radialposition of the IC is provided. A duty factor table can be provided inplace of the duty factor calculator 60. Based on the result of thecalculation result of the duty factor calculator 60, the microprocessor58 controls the read/write controller 51 to secure a predetermined valueof the duty factor corresponding to the radial position of the IC,thereby supplying the predetermined power to the head IC 52 for apredetermined length of time (corresponding to the duty factor). Thus,like in the first embodiment, the temperature rise of the IC issuppressed within the tolerable value, while at the same time making itpossible to maximize the IC efficiency, i.e. the read/write performanceof the head unit.

[0042] The third embodiment of the invention will be explained withreference to FIGS. 7, 8 and Table 3. FIG. 7 shows the relation betweenthe response time and the thermal resistance Rh (calorific valueW/temperature rise K) determined by the Reynolds number Rew of rotation,and FIG. 8 the relation between the dimensionless time and thetemperature change. These diagrams are based on the formulae determinedby the experiments conducted by the inventors. Assume that the tolerabletemperature rise of the IC is 50 K and the rated power of the IC is 400mW. The time required before reaching 50 K assumes the values shown inTable 3. TABLE 3 Reynolds Tolerable Tolerable number Rew of time(s) attime(s) at IC position rotation 400 mW 500 mW Inner periphery 5.3 × 10⁴0.17 0.13 Middle 8.1 × 10⁴ 0.19 0.13 periphery Outer 12.1 × 10⁴  0.200.13 periphery

[0043] As shown in Table 3, the values are substantially the same forthe inner and outer peripheries, although the value for the outerperiphery is somewhat longer than the value for the inner periphery.These values are 0.17 s, 0.19 s and 0.2 s for the inner periphery, themiddle periphery and the outer periphery, respectively. This indicatesthat by reducing the continuous conduction time to 0.17 s or less, theIC temperature rise can be reduced to lower than the tolerabletemperature even when the rated power of 400 mW is supplied, therebyproducing the same effect as the first embodiment. Also, in the casewhere the rated power of the IC is 500 mW, the continuous conductiontime may be set to 0.13 s or less.

[0044] A fourth embodiment of the invention will be explained withreference to FIGS. 9 and 10. The difference between this embodiment andthe first embodiment lies in that as shown in FIG. 9, the presentembodiment has two head ICs 30 a and 30 b mounted. Also, as shown inFIG. 10, each head IC has a temperature sensor. The use of two ICs makesit possible to switch to the IC 52 b when the other IC 52 a approachesthe tolerable temperature rise as detected by the temperature sensor. Asa result, the same effect as the second embodiment is achieved.Specifically, as viewed from the magnetic head unit, power iscontinuously supplied from the IC to the magnetic head unit, andtherefore the continuous read/write operation is possible. Also, fromthe viewpoint of the IC temperature rise, the alternate use of the twoICs is equivalent to the fact that one of the ICs is suspended inoperation and can be cooled during the suspension time. Therefore, inthe case where the two ICs are switched for every 0.17 s for the innerperiphery, for example, as shown in the third embodiment, the sameeffect is obtained as if the IC is apparently continuously used at therated power.

[0045] The experiments conducted by the inventors show that thetemperature rise due to heating and the cooling due to the heatradiation last for substantially the same length of time. The use of twoICs alternately as described above, therefore, can prevent the faultyoperation which otherwise might be caused by the temperature rise due tothe heating of the IC itself. The effect of the present embodiment isespecially significant for a magnetic disk device having a singlemagnetic head mounted thereon. Specifically, with the magnetic disk unitdevice having a plurality of magnet heads mounted thereon, in the casewhere the temperature of the IC of one of the magnetic heads increasesbeyond the tolerable value, the operation is switched to the othermagnetic head unit to record the data with the particular other magnetichead unit (other IC).

[0046] In the case where only one magnetic head is provided and theother magnet head is unavailable for use, on the other hand, theavailable magnetic head is used with a lower duty factor as in thesecond embodiment, or the suspension time is inserted as in the thirdembodiment, resulting in the deteriorated performance of the read/writeoperation. On the other hand, the present embodiment using two ICsexhibits an especially high effect for the magnetic disk device havingonly one head. Also, the present embodiment is effective especially inthe case where the two magnetic heads, if any, of the magnetic head unitcannot be switched, i.e. in the case where the continuous read/writeoperation is required with a single head.

[0047] In the aforementioned embodiments, the IC is arranged on theouter peripheral side at the forward end of the guide arm. As shown inFIGS. 11A, 11B, however, the IC can be mounted on the suspension meansor on the inner peripheral side at the forward end of the guide arm withequal effect. In the case where the IC is mounted on the suspensionmeans as shown in FIG. 11A, the heat conduction to the suspension meansincreases and the cooling performance is improved. In the case where theIC is mounted on the inner peripheral side of the magnetic disk 4 asshown in FIG. 11B, on the other hand, the advantage is that the coolingperformance (heat conduction) by the air flow is improved.

[0048] According to the embodiments described above, the temperature ofthe signal amplifier (IC) mounted on the magnetic head supportingmechanism can be controlled to not higher than a predeterminedtemperature without any special cooling means. Therefore, a large volumeof information can be recorded/reproduced at high speed while securingreliability.

1. A magnetic disk device comprising a magnetic disk for recordinginformation, a rotary mechanism for rotating said magnetic disk, amagnetic head unit for recording information on the rotating magneticdisk, a slider having mounted thereon said magnetic head unit and flyingover said rotating magnetic disk, a magnetic head supporting mechanismfor supporting said slider, and a positioning mechanism for setting saidmagnetic head unit at a predetermined radial position, wherein saidmagnetic head supporting mechanism has mounted thereon an integratedcircuit (IC) for amplifying an information write/read signal of saidmagnetic head unit, and a control circuit is connected to said IC, andwherein said control circuit controls a record frequency according tothe radial position of said IC on said magnetic disk.
 2. A magnetic diskdevice according to claim 1, wherein said control circuit operates sothat the record frequency is higher when said IC is located at an outerperipheral position of said magnetic disk than when said IC is locatedat an inner peripheral position of said magnetic disk.